The main purpose of the proposed study is to determine if there are specific abnormalities in brain stem structures that contribute to the genesis of the sudden infant death syndrome (SIDS). To accomplish this aim we propose to undertake quantitative histologic and histochemical studies on brain stem structures that regulate respiration and other vital functions. A variety of clinical and postmortem findings point to brain stem structures as the possible origin of SIDS. Specifically we propose to determine if any of the following are present in specific brain structures of SIDS victims: (1) abnormalities in dendrities, (2) an abnormal number of neurons in the following cranial nerve nuclei: 6th, 7th, 10th, 12th, (3) presence of astrocytosis (4) retardation of myelination. We propose to determine the relationship of any abnormalities found in the brain stem of SIDS victims to previously discovered postmortem abnormalities in SIDS victims that are markers of chronic alveolar hypoxia and hypoxemia. These include measurements of the amount of muscle in small pulmonary arteries, abnormally retained brown fat around the adrenal glands and hepatic erythropoiesis. We also propose to correlate brain stem abnormalities with the presence or absence of carotid body hypoplasia, another common abnormality in SIDS victims. It is also planned to determine if any brain stem abnormalities that are found are secondary to chronic hypoxemia by seeing if such abnormalities exist in infants who have died as the consequence of cyanotic heart disease.